This disclosure relates to polyetherimides and compositions containing the polyetherimides, as well as their method of manufacture and articles formed from the polyetherimide compositions.
Polyetherimides (“PEIs”) are amorphous, transparent, high performance polymers having a glass transition temperature (“Tg”) of greater than 180° C. PEIs further have high strength, heat resistance, and modulus, and broad chemical resistance, and so are widely used in applications as diverse as automotive, telecommunication, aerospace, electrical/electronics, transportation, and healthcare.
Polyetherimides can be manufactured commercially by a “halo-displacement process.” As shown in FIG. 1, a halogen-substituted anhydride is reacted with a diamine to form a bishalophthalimide. The bishalophthalimide is then reacted with a metal salt of a dihydroxy compound. Despite extensive investigation into the manufacture of polyetherimides produced using the halo-displacement process, there nonetheless remains a need for further improvement. For example, some polyetherimides are currently manufactured using a 95:5 ratio of the 4-isomer to the 3-isomer of the halophthalic anhydride, which yields a product having excellent ductility. Increasing the relative ratio the 3-isomer can enhance flow and Tg of the polyetherimides, but above 50%, the cyclic n=1 byproduct dramatically increases from non-detectable to 1.5 to 15% by weight. These high levels can be detrimental, because the low molecular weight cyclic can act as plasticizer, thereby reducing the Tg. The low molecular weight cyclic byproduct also can diffuse out of molded parts at aggressive molding conditions, causing splay and other issues.
There accordingly remains a need in the art for methods for the manufacture of polyetherimides having improved properties, in particular polyetherimides having improved Tg and flow, but with reduced levels of byproducts, including halogenated byproducts and cyclic byproducts. It would be a further advantage if such improvements were obtained without significantly adversely affecting other desirable properties of the polyetherimides, for example one or more of heat deflection temperature, Vicat, and high tensile strength at yield.